The invention lies in the electronics field. More specifically, the invention relates to a bandpass filter, particularly for use in circuits using RF technology.
In many circuit configurations using RF technology, for example in circuit configurations for contiguous division of a relatively large frequency range (e.g. the TV frequency range) into a plurality of smaller frequency bands, bandpass filters are required which have a comparatively large pass bandwidth, with, at the same time, comparatively steep edges up to the stop band and low attenuation in the passband.
French patent document FR 952403 discloses a bandpass filter circuit. There, a capacitor is connected in series with a parallel LC element. The filter four-terminal circuit has an additional parallel LC element at the output.
U.S. Pat. No. 5,483,209 discloses a circuit for changing over between different reception bands with variable attenuation control. The circuit has a plurality of bandpass filters tuned to the different input reception frequencies. In addition, the circuit has a plurality of variable attenuation diodes whose impedances are controlled by means of an AGC. A plurality of switching diodes are used to select the bandpass filter tuned-to the input signal.
It is accordingly an object of the invention to provide a bandpass filter, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which satisfies the aforementioned requirements.
With the foregoing and other objects in view there is provided, in accordance with the invention, a bandpass filter, comprising:
a bandpass filter input and a bandpass filter output;
a series circuit connected between the bandpass filter input and the bandpass filter output, the series circuit being formed of a first capacitor, a first parallel LC element connected to the first capacitor, a second capacitor connected to the first parallel LC element, and an inductor connected to the second capacitor;
a second parallel LC element having a first connection connected to a node between the first parallel LC element and the second capacitor and a second connection coupled to a fixed reference-ground potential via a third capacitor; and
a third parallel LC element having a first connection connected to a node between the second capacitor and the inductor and a second connection coupled to the fixed reference-ground potential, either directly or via a fourth capacitor connected between the second connection of the third parallel LC element and the fixed reference-ground potential.
In accordance with an additional feature of the invention, a fifth capacitor is connected to a node between the second capacitor and the inductor and to the fixed reference-ground potential.
With the above and other objects in view there is also provided, in accordance with the invention, a circuit configuration, comprising:
an AC voltage input terminal and an AC voltage output terminal;
a plurality of frequency domain filter paths defined between the AC voltage input terminal and the AC voltage output terminal, and connected in parallel between a common first node and a common second node both coupled to a DC voltage connection;
each of the frequency domain filter paths containing at least one of the above-outlined bandpass filters connected in series with a first diode and a second diode connected in opposite forward direction from the first diode;
each of the frequency domain filter paths containing a switching unit for switching the first and the second diode in the frequency domain filter path during an operation of the circuit configuration for turning a respective one of the bandpass filters;
a third diode having a first terminal connected to the first node and a fourth diode having a first terminal connected to the second node of the frequency domain filter paths, such that a respective cathode of the third diode and of the fourth diode is connected to anodes of the first diodes and the second diodes, respectively;
a load-dependent DC voltage source having a first connection and a second connection; and
the third diode and the fourth diode each having a second terminal respectively connected to the first connection and the second connection of the load-dependent DC voltage source.
In accordance with another feature of the invention, the first, second, third, and fourth diodes are PIN diodes.
In accordance with a further feature of the invention, each of the switching units includes:
a first electrical resistor and a second electrical resistor respectively connected, via a first terminal thereof, to the input and to the output of an associated one of the frequency domain filters, and to one another via a second terminal thereof;
an on/off switch having a first terminal connected between the first electrical resistor and the second electrical resistor, and a second terminal connected to a fixed reference-ground potential; and
a capacitor having a first terminal connected between the first electrical resistor and the second electrical resistor, and a second terminal connected to the fixed reference-ground potential.
In further summary, in the bandpass filter according to the invention:
a) a series circuit, comprising a first capacitor, a first parallel LC element, a second capacitor and an inductor, is connected between a bandpass filter input and a bandpass filter output, the individual elements in the series circuit being connected one after the other in the aforementioned sequence;
b) a second parallel LC element, whose second connection is coupled to a fixed reference-ground potential via a third capacitor, is connected in a connection line between the first parallel LC element and the second capacitor; and
c) a third parallel LC element, whose second.connection is coupled to the fixed reference-ground potential directly or via a fourth capacitor, is connected in a connection line between the second capacitor and the inductor.
Optionally, the connection line between the second capacitor and the inductor is coupled to the fixed reference-ground potential (e.g. ground) via a fifth capacitor.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a bandpass filter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.